In the agricultural sector methyl bromide is commonly used to limit the growth of fungal pathogens, nematodes, wireworms, insects, bacteria and weeds. However, methyl bromide has a relatively high environmental impact: reacting with the ozone present in the upper layer of the atmosphere, it transforms it into Br2O, contributing to destruction of the ozone.
Recently, to replace methyl bromide, molecules of vegetable origin with cytotoxic activity for soil pathogens and parasites have been proposed. Among these molecules, derivatives of glucosinolates (GLs) generated by hydrolysis catalysed by the enzyme myrosinase (MYR) or by thermolysis have been proposed. The GLs are anionic thioglucosidic compounds present in variable quantities and ratios in a number of organisms and vegetable tissues. The molecular structure of the approximately 120 GLs currently isolated and characterised consists of a common functional group and a lateral chain which can be of aliphatic, aromatic or heteroaromatic type.
The GLs, in the presence of the enzyme MYR (thioglucoside glucohydrolase, EC 3.2.3.1), are hydrolysed with formation of β-D-glucose, sulphate ion and a number of derivatives such as isothiocyanates, nitrites or thiocyanates (see, for example, Tookey H. L., Van Etten C. H., Daxembichler M. E., Toxic Constituent of Plant Foodstuffs, edited by I. E. Liner, 1980, II edition, 4, 103-142).
Some of the above-mentioned derivatives of the GLs, in particular the isothiocyanates, have shown in vitro cytotoxic properties towards nematodes (see Lazzeri L., Tacconi R., Palmieri S., In Vitro Activity of Some Glucosinolates and Their Reaction Products toward a Population of the Nematode Heterodera schachtii, J. Agric. and Food Chem. 1993, 41, 825-829) and plant fungal pathogens present in the soil (see, for example, Manici L. M., Leoni O., Lazzeri L., Galletti S., Palmieri S., Fungitoxic Activity of Some Glucosinolate Enzyme Derived Products Against the Main Soil-Borne Pathogens, Pesticide Science, 1999, 55, 486-488; and Manici L. M., Lazzeri L., Palmieri S., In Vitro Fungitoxic Activity of Some Glucosinolates and their Enzyme-derived Products toward Plant Pathogenic Fungi, J. Agric. and Food Chem. 1997, 45, 2768-2773).
To obtain and use the above-mentioned derivatives of the GLs, extraction and/or production procedures are necessary, which are relatively complex and costly and can also cause environmental problems (for example disposal of the by-products and/or the solvents used). Furthermore, generally some important derivatives of the GLs (for example allylisothiocyanate) are relatively difficult to handle as they have a relatively high volatility. To overcome these negative aspects the technique of green manure of plants containing both GLs and the enzyme MYR (i.e. containing the GLs-MYR system) has been proposed.
The green manure technique of plants containing the GLs-MYR system has some negative aspects, however, typical of the green manure technique in general. In particular, the green manure technique requires cultivation operations that determine relatively high labour costs and causes the loss of at least one growing cycle, with consequent damage for the farmer due to loss of income.